The present invention relates to a method and an apparatus for enhancing the impact created by a drilling jar used downhole when the drill string becomes stuck.
Drilling jars are used widely in the drilling industry to allow a jarring impact to be transmitted to the drill string when, for example, the drill string becomes stuck in the borehole in which the drilling operation is being performed.
Drilling jars may be incorporated into a bottom hole assembly of a drill string and comprise an outer tubular housing which surrounds an inner tubular member. The outer tubular housing may be connected at its lower end to the lower portion of the drill string while the upper end of the inner tubular member is connected to the upper portion of the drill string. The inner member and outer housing are telescopically connected such that one may move axially with respect to the other. Generally, the inner member of a drilling jar has an abutment that acts as a hammer and coincides with an internal shoulder provided on the outer housing of the jar that acts as an anvil such that the free stroke of the inner member with respect to the outer housing causes the hammer to impact against the anvil. This impact causes the lower drill string portion to jar.
The impact momentum (also referred to as “impact force”) created by the jar is the speed of the hammer multiplied by the hammer weight at the time of impact, where the hammer weight is the weight of any drill collars and/or heavy weight pipe located between the jar hammer and drill pipe or energizer.
The impact force between the hammer and anvil may be increased using an impact enhancing tool that employs energy storage means that can be used to store energy, which when suddenly released causes the inner member of the jar to accelerate with respect to the outer housing of the jar, while the hammer is moving toward the anvil.
Unfortunately, in conventional drilling strings, the pins and boxes are subject to stretching both when the tubular members are connected and during drilling.
What is needed, therefore, is an apparatus and a methodology that address at least one if not more of the deficiencies that afflict conventional practice, as previously described.